1. Field of the Invention
A sulfur recovery plant is provided comprising a primary Claus reactor and a plurality of downstream reactor units, each reactor unit comprises a reactor that is selectively operable under Claus reaction conditions and cold bed adsorption (CBA) reaction conditions thereby permitting the plant to achieve greater than 99.5% average sulfur removal efficiency. The high sulfur removal efficiencies are obtained through sequencing the reactor units such that the reactor unit containing the coolest catalyst is positioned in the final spot in the series of reactor units. The order of reactor units within the sequence is periodically changed so as to permit catalyst regeneration. However, the reactor unit containing the newly regenerated catalyst is shifted to a middle position, as opposed to the final position in the sequence of reactor units. This manner of shifting the order of reactor units within the plant provides additional cooling time for the catalyst that has been most recently regenerated thereby ensuring that the final reactor unit in the series is capable of highly efficient cold bed adsorption operation.
2. Description of the Prior Art
The processing of natural gas or petroleum products often results in the generation of acid gas streams comprising oftentimes significant quantities of sulfur, generally in the form of H2S. These acid gas streams are often of limited value and are commonly disposed of by incineration. However, environmental regulations restrict the amount of sulfur that can be released into the atmosphere. Therefore, a significant portion of the sulfur present in these waste product streams must be removed prior to incineration.
One approach to the removal of sulfur has been through the use of an extended Claus sulfur recovery plant, such as that disclosed in U.S. Pat. Nos. 5,015,459 and 5,015,460. In these plants, one catalytic reactor is operated under high temperature Claus conditions in series with one or more catalytic reactors each periodically operated under high temperature Claus and cold bed adsorption (CBA) conditions. Each catalytic reactor that alternates between Claus conditions and CBA conditions is associated with a sulfur condenser to comprise a reactor unit. The sequencing of the reactor units is periodically changed so that the reactor having freshly-regenerated catalyst is placed in the last position in the sequence.
The CBA plants have demonstrated average sulfur removal efficiencies of up to 99.2%. However, as environmental regulations become even more strict, CBA plants such as those described in the aforementioned patents have not thus far been able to achieve 99.5% or greater average sulfur reduction efficiencies. In order to achieve this level of efficiency, conventional CBA plants would need to be equipped with an additional tail gas treating unit, such as a hydrogenation/amine treating unit, thereby adding further capital and operating expense. Thus, it would be highly desirable if a CBA plant could be configured to achieve 99.5% or greater average sulfur removal efficiency without the need for additional tail gas treatment.